In recent years, mobile phones and other devices which reproduce sound have mounted noise suppressors for suppressing noise included in the received audio signal so as to improve the quality of the reproduced sound. To improve the quality of the reproduced sound, a noise suppressor preferably accurately discriminates between the voice of the speaker or other audio signal to originally be reproduced and noise.
Therefore, art is being developed for analyzing a frequency spectrum of an audio signal so as to judge the type of sound which is included in the audio signal (for example, see Japanese Laid-Open Patent Publication No. 2004-240214, Japanese Laid-Open Patent Publication No. 2004-354589 and Japanese Laid-Open Patent Publication No. 9-90974).
However, it is difficult to detect noise of the combined speaking voices of a plurality of persons conversing in the background, that is, “babble noise”. For this reason, when an audio signal includes babble noise, sometimes the noise suppressor cannot effectively suppress the babble noise.
Therefore, art has been proposed for separately detecting babble noise from other noise (for example, see Japanese Laid-Open Patent Publication No. 5-291971).